Semiconductor light emitting device with transparent electrode having holes

ABSTRACT

A semiconductor light emitting device and a fabrication method thereof includes: providing a substrate; forming an n-type semiconductor layer, a light emitting layer, a p-type semiconductor layer on the substrate; forming a first transparent electrode having holes per a certain region on the p-type semiconductor layer; and forming a first pad on the first transparent electrode.A method of fabricating a semiconductor light emitting device, and which includes forming a light emitting layer on the first type semiconductor layer; forming a second type semiconductor layer on the light emitting layer; forming a first transparent electrode on the second type semiconductor layer, the first transparent electrode having holes per a certain region to thereby expose the second type semiconductor layer; forming a second transparent electrode on the first transparent electrode; forming a first pad on the second transparent electrode; and forming a second pad over the first type semiconductor layer. Further, the first transparent electrode is in the shape of columns with gaps therebetween on the second type semiconductor layer, and the second transparent electrode completely covers the first transparent electrode and fills the gaps of the first transparent electrode.

This application is a reissue of U.S. Pat. No. 7,109,048 B2 issued onSep. 19, 2006, and the entire contents of the patent are herebyincorporated by reference.

This Nonprovisional application claims priority under 35 U.S.C. § 119(a)on patent application Ser. No(s). 10-2003-0067968 and 10-2003-0067802filed in Korea, Republic of on Sep. 30, 2003, the entire contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor light emitting device,and more particularly, to a semiconductor light emitting device capableof maximizing an emission of light generated at a light emitting layerto outside and easily spreading a current to the light emitting layer,and a fabrication method thereof.

2. Description of the Related Art

Generally, a semiconductor is a direct transition type, and has beenused to form a light emitting wavelength from a red region to a purpleregion and an ultraviolet ray region due to a high light emittingefficiency. As the understanding for a growing method and a structure ofthe semiconductor is increased, characteristics of a light emittingdevice, that is, a brightness, a driving voltage, or a staticcharacteristic have been improved.

However, in spite of these efforts, a high output and a low drivingvoltage are much required, and a nitride semiconductor light emittingdevice that outputs a long wavelength (yellow and red) and a shortwavelength (ultraviolet rays) has to be continuously researched. FIG. 1shows a structure of a nitride semiconductor light emitting device inaccordance with the conventional art.

As shown, the conventional nitride semiconductor light emitting devicecomprises: a sapphire substrate 10; an n-doped GaN layer 11 on thesapphire substrate 10; a light emitting layer 12; a p-GaN layer 13; atransparent electrode 14 formed on the p-GaN layer 13; a p-pad electrode15 on the transparent electrode 14; and an n-pad electrode 16 formed onthe n-GaN layer 11 exposed by vertically mesa-etching from the p-GaNlayer 13 to a part of the n-GaN layer 11.

FIG. 2 is a view showing a structure of another nitride semiconductorlight emitting device, that is, a Top-down electrode type semiconductorlight emitting device in accordance with the conventional art. As shown,on a silicon carbide (SiC) substrate 20, an n-GaN layer 21, a lightemitting layer 22, a p-GaN layer 23, and a transparent electrode 24 aresequentially formed. An n-pad electrode 26 is formed below the siliconcarbide substrate 20, and a p-pad electrode 25 is formed on thetransparent electrode 24.

In the conventional nitride semiconductor light emitting device, thetransparent electrode lowers a driving voltage of a device byfacilitating a current spread, and enhances a quantum efficiency byemitting light generated at a light emitting layer to outside. As thetransparent electrode, a metal such as Ni or Au, or a TCO-based oxidesuch as ITO or IZO are used.

In case of using a metal such as Ni or Au as the transparent electrode,a current spread to the p-GaN layer can be facilitated by lowering anohmic contact resistance of the p-GaN layer. However, a metal oxidegenerated at the time of depositing the transparent electrode preventslight generated from a light emitting layer from being emittedoutwardly, thereby lowering a light transmittance.

Therefore, in order to increase the light transmittance, a TCO-basedoxide such as ITO or IZO is used. However, in case of using theTCO-based oxide, a contact resistance between a P-type nitridesemiconductor layer and a TCO electrode is very great thereby toincrease a driving voltage.

The transparent electrode can be formed as a layer more than two byusing a metal oxide generating metal such as Ni, Pd, Pt, etc. and acurrent spreading metal such as Au, etc. As the transparent electrode,Ni and Au are mainly used.

For example, a first metal layer is deposited on the p-GaN layer byusing the metal oxide generating metal, Ni, and then a second metallayer is deposited on the first metal layer by using a current spreadingmetal, Au, thereby forming a transparent electrode.

At this time, a metal oxide such as NiO is formed as said Ni isoxidized. The metal oxide supplies a hole to the p-GaN layer.

However, since said metal oxide has an inferior conductivity, a spreadof a current supplied from outside to the light emitting layer isprevented. According to this, it is necessary to prevent the metal oxidefrom being excessively formed.

However, in said general method, that is, in a method for forming atransparent electrode by depositing a metal layer more than two layerson a p-GaN by a separate deposition process, much metal oxide isentirely generated from an interface between the p-GaN layer and themetal layer to the uppest metal layer.

FIG. 3 schematically shows a sectional surface of a transparentelectrode formed on a P-type nitride semiconductor in accordance withthe conventional art. Referring to FIG. 3, GaN, III-V group compound isformed on a sapphire substrate, then Ni and Au are sequentiallydeposited on the p-doped GaN layer, and then a thermal annealing isperformed to obtain a transparent electrode.

As shown, when the thermal annealing is performed after sequentiallydepositing Ni and Au, Au of an island shape is formed on the p-doped GaNlayer 13 and the Ni is oxidized thereby to form an oxide metal. At thistime, the metal oxide supplies a hole to a p-GaN layer, and said Aufacilitates a spread of the hole supplied from the metal oxide to thelight emitting layer.

FIG. 4 is a view showing a distribution of Au and NiO according to athickness of a transparent electrode in accordance with the conventionalart. In the experiment, a sapphire substrate was used as a substrate, aGaN, III-V group compound was used as a nitride semiconductor, Ni and Auwere sequentially deposited on the p-doped GaN layer to form atransparent electrode, and a thickness of the transparent electrode wasapproximately 1 nm˜100 nm. Also, a thermal annealing for forming thetransparent electrode was performed at a temperature of approximately600° C., and an allowance error range of the temperature in the thermalannealing was approximately ±100° C. At this time, the thermal annealingwas performed in an atmosphere that a little amount of oxygen is mixedto nitrogen, and a rapid thermal annealing (RTA) device was used for thethermal annealing.

As shown from the graph, Au is concentrated on the surface of the P-GaN,and NiO is decreased from the surface thereof to the interface betweenthe P-GaN. Also, on the surface of the P-GaN, Au and NiO are similarlydistributed.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a nitridesemiconductor light emitting device capable of maximizing an emission oflight generated at a light emitting layer to outside, and a fabricationmethod thereof.

Another object of the present invention is to provide a nitridesemiconductor light emitting device capable of facilitating a currentspread to a light emitting layer of a semiconductor light emittingdevice, and a fabrication method thereof.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described herein,there is provided a fabrication method of a semiconductor light emittingdevice comprising: providing a substrate; sequentially forming an n-typesemiconductor layer, a light emitting layer, a p-type semiconductorlayer on the substrate; forming a first transparent electrode havingholes per a certain region on the p-type semiconductor layer; andforming a first pad on the first transparent electrode.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described herein,there is also provided a semiconductor light emitting device comprising:an n-type semiconductor layer formed on the substrate; a light emittinglayer formed on the n-type semiconductor layer; a p-type semiconductorlayer formed on the light emitting layer; a first transparent electrodehaving holes per a certain region on the p-type semiconductor layer; anda first pad formed on the first transparent electrode.

According to another embodiment of the present invention, a fabricationmethod of a semiconductor light emitting device comprises: providing asubstrate; sequentially forming an n-type semiconductor layer, a lightemitting layer, a p-type semiconductor layer on the substrate;depositing a metal group that at least one metal oxide generating metaland at least one current spreading metal are mixed on the p-typesemiconductor layer, and thereby forming a first transparent electrode;and forming a first pad on the p-type semiconductor layer.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIGS. 1 and 2 show one embodiment of a nitride semiconductor lightemitting device in accordance with the conventional art;

FIG. 3 is a graph schematically showing a structure of a transparentelectrode of the nitride semiconductor light emitting device inaccordance with the conventional art;

FIG. 4 is a view showing a distribution of Au and NiO formed on a P-typesemiconductor in accordance with the conventional art;

FIGS. 5A to 5E are processing section views showing a fabrication methodof a semiconductor light emitting device according to one embodiment ofthe present invention;

FIG. 6 is a view taken along line A-A of FIG. 5E;

FIGS. 7A to 7D are processing section views showing a fabrication methodof a semiconductor light emitting device according to a secondembodiment of the present invention;

FIG. 8 is a view taken along line B-B of FIG. 7D;

FIGS. 9A to 9D are processing section views showing a fabrication methodof a semiconductor light emitting device according to a third embodimentof the present invention;

FIGS. 10A to 10C are processing section views showing a fabricationmethod of a semiconductor light emitting device according to a fourthembodiment of the present invention;

FIG. 11 is a view schematically showing a structure of a transparentelectrode of a semiconductor light emitting device according to thepresent invention; and

FIG. 12 is a graph showing a distribution of Au and NiO formed on ap-type semiconductor according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

Hereinafter, a nitride semiconductor light emitting device and afabrication method thereof according to the present invention will beexplained with reference to the attached drawings.

FIGS. 5A to 5E are processing section views showing a fabrication methodof a semiconductor light emitting device according to one embodiment ofthe present invention.

As shown in FIG. 5A, according to one embodiment of the presentinvention, an n-type nitride semiconductor layer 31, a light emittinglayer 32, and a p-type nitride semiconductor layer 33 are sequentiallyformed on a substrate 30.

That is, a nitride semiconductor layer is grown on the substrate 30 byusing a metal organic vapor phase epitaxy growing method, etc. Then, ann-type impurity is doped thereby to form the n-type nitridesemiconductor layer 31. Next, the light emitting layer 32 and a nitridesemiconductor layer are sequentially deposited on the n-type nitridesemiconductor layer 31, then the nitride semiconductor layer is grownwith a certain thickness, and a p-type impurity is doped, therebyforming the p-type nitride semiconductor layer 33.

The substrate 30, a hetero-substrate may be formed of a sapphiresubstrate or a silicon carbide (SiC) substrate.

The n-type nitride semiconductor layer 31 can be formed with a thicknesscorresponding to 1 μm˜500 μm, approximately. As the n-type impurity, oneof Si, Ge, Se, S, Te, etc. can be selected.

The p-type nitride semiconductor layer 33 may be formed of GaN, AlGaN,and InGaN with a thickness corresponding to 0.1 μm˜100 μm,approximately. As the p-type impurity, one of Be, Sr, Ba, Zn, Mg, etc.can be selected.

When the n-type nitride semiconductor layer 31, the light emitting layer32, and the p-type nitride semiconductor layer 33 are sequentiallyformed on the substrate 30, a mesa etching is partially performed fromthe p-type nitride semiconductor layer 33 to the n-type nitridesemiconductor layer 31 in a vertical direction. According to this, asshown in FIG. 5B, a part of the n-type nitride semiconductor layer 31 isexposed.

Then, on the p-type nitride semiconductor layer 33 that remains withoutbeing etched in said etching process, one transparent conductive metalof Ni, Au, Pd, Pt, Pu, Ir, etc. or a mixture of at least twotherebetween is deposited thereby to form a single metal layer or amulti-metal layer. Then, the deposited metal layer is patterned therebyto form a first transparent electrode 34 having a plurality of holes 34arepeatedly-formed per a certain region, as shown in FIG. 5C. Herein, theterm of ‘transparent’ denotes the time when a light transmittance ismore than 10%, which does not denote no color or a transparency.

Then, as shown in FIG. 5D, a transparent conducting oxide (TCO)-basedsecond transparent electrode 35 can be formed on the first transparentelectrode 34 where the holes 34a are repeatedly patterned per a certainregion. That is, the TCO-based oxide, for example, one oxide selectedfrom a group of ITO, IZO, ZnO, AZO, CdO, MgO, etc. is deposited andthermally annealed thereby to form the second transparent electrode 35.

The second transparent electrode 35 is for enhancing an emissionefficiency of light generated at the light emitting layer 32 thus to beemitted from the first transparent electrode 34 and the holes 34 tooutside. That is, when light generated from the light generating layer32 by a current supplied from outside is emitted to the secondtransparent electrode 35 through the first transparent electrode 34 andthe hole 34a, an outside area that the emitted light can reach isobtained to the maximum thereby to facilitate an emission of the lightto outside.

Finally, on the respective second transparent electrode 35 and theexposed n-type nitride semiconductor layer 31a, one of Ni, Cr, Al, Au,Pt, Ti, etc. or a mixture of at least two therebetween is deposited andthen is patterned. According to this, as shown in FIG. 5E, a first pad36 for electrically connecting the second transparent electrode 35 to anexternal terminal, and a second pad 37 for electrically connecting theexposed n-type nitride semiconductor layer 31a to an external terminalare respectively formed.

When the second transparent electrode 35 is not formed, the first pad 36is formed on the first transparent electrode 34. In the presentinvention, the second transparent electrode 35 can be formed or can notbe formed.

FIG. 6 is a view taken along line A-A of FIG. 5E, which shows a nitridesemiconductor light emitting device fabricated according to the firstembodiment of the present invention.

As shown, the nitride semiconductor light emitting device according tothe present invention comprises: a substrate 30; an n-type nitridesemiconductor layer 31 formed on the substrate 30; a light emittinglayer 32 formed on the n-type semiconductor layer 31; a p-typesemiconductor layer 33 formed on the light emitting layer 32; a firsttransparent electrode 34 formed as a transparent electrode forming metalis deposited on the p-type semiconductor layer 33 and then is patternedso that holes are repeatedly formed per a certain region; a secondtransparent electrode 35 formed on the first transparent electrode 34;and first and second pads 36 and 37 respectively formed on the secondtransparent electrode 35 and the n-type semiconductor layer 31.

Since the first transparent electrode 34 is formed of a transparentconductive metal, an ohmic contact resistance of the p-type nitridesemiconductor layer 33 is lowered thereby to facilitate a spread of acurrent supplied from an external power source thus to be transmitted tothe first transparent electrode 34 through a pad electrode formed in thelater process to the light emitting layer 32.

Therefore, when compared to the conventional art in which the TCOelectrode is used as a transparent electrode, in the present invention,a driving voltage can be more lowered since a contact resistance betweenthe p-type nitride semiconductor layer and the TCO electrode is less.That is, in the present invention, since a current spread to the lightemitting layer can be facilitated, a spread of the same amount ofcurrent to the light emitting layer can be performed even with a drivingvoltage lower than the conventional driving voltage.

Also, in the present invention, holes are formed per a certain region onthe transparent electrode, so that a light transmittance can be moreincreased when compared to the conventional case that Ni and Au areused. That is, in the conventional art, the hole region is not formed.Therefore, when a certain amount of current is supplied to the lightemitting layer, a metal oxide generated on the transparent electrodelayer shields a part of light generated from the light emitting layerthus to be emitted to outside thereby to lower a light transmittance. Onthe contrary, in the present invention, even if a metal oxide forshielding a light emission is generated on the transparent electrodelayer, a light transmittance to outside can be increased since holes areformed per a certain region on the transparent electrode layer.

That is, in the present invention, in order to prevent a phenomenon thatlight emitted outwardly is decreased since a light transmittance islowered due to a metal constituting the first transparent electrode, anarea occupied by a metal at the first transparent electrode is minimizedwith maintaining an ohmic contact and holes are formed at the rest partfor a light transmittance. According to this, light can be easilyemitted upwardly.

In the present invention, a transparent conductive metal is deposited onthe p-type nitride semiconductor layer deposited on the light emittinglayer, and then is patterned thereby to form the first transparentelectrode having a plurality of holes. According to this, a currentsupplied from outside can be easily spread to the light emitting layerthrough a pad electrode formed in the later process, and light generatedfrom the light emitting layer can be easily emitted to outside throughthe hole formed per a certain region.

The present invention can be also applied to a Top-down electrode typesemiconductor light emitting device where a silicon carbide (SiC)substrate is used.

FIGS. 7A to 7D are processing section views showing a fabrication methodof a semiconductor light emitting device according to a secondembodiment of the present invention applied to a Top-down electrode typesemiconductor light emitting device.

As shown in FIG. 7A, according to the second embodiment of the presentinvention, an n-type nitride semiconductor layer 41, a light emittinglayer 42, and a p-type nitride semiconductor layer 43 are sequentiallyformed on a substrate 40.

That is, a nitride semiconductor layer is grown on the substrate 40 byusing a metal organic vapor phase epitaxy growing method, etc. Then, ann-type impurity is doped thereby to form the n-type nitridesemiconductor layer 41. Next, the light emitting layer 42 and a nitridesemiconductor layer are sequentially deposited on the n-type nitridesemiconductor layer 41, then the nitride semiconductor layer is grownwith a certain thickness, and a p-type impurity is doped, therebyforming the p-type nitride semiconductor layer 43.

The substrate 40, a hetero-substrate may be formed of a silicon carbide(SiC) substrate.

Then, on the p-type nitride semiconductor layer 43, one transparentconductive metal of Ni, Au, Pd, Pt, Pu, Ir, etc. or a mixture of atleast two therebetween is deposited thereby to form a single metal layeror a multi-metal layer. Then, the deposited metal layer is patternedthereby to form a first transparent electrode 44 having a plurality ofholes 44a repeatedly-formed per a certain region, as shown in FIG. 7B.

Then, as shown in FIG. 7C, a transparent conducting oxide (TCO)-basedsecond transparent electrode 45 is formed on the first transparentelectrode 44. That is, the TCO-based oxide, for example, one oxideselected from a group of ITO, IZO, ZnO, AZO, CdO, MgO, etc. is depositedon the first transparent electrode 44 and thermally annealed at atemperature of 400° C.˜1000° C. thereby to form the second transparentelectrode 45.

Then, as shown in FIG. 7D, on the second transparent electrode 45 and onthe rear surface of the substrate 40, one of Ni, Cr, Al, Au, Pt, Ti,etc. or a mixture of at least two therebetween is deposited and then ispatterned. According to this, as shown in FIG. 5E, a first pad 46 forelectrically connecting the second transparent electrode 45 to anexternal terminal, and a second pad 47 for electrically connecting thesubstrate 40 to an external terminal are respectively formed.

FIG. 8 is a view taken along line B-B of FIG. 7D, which shows asemiconductor light emitting device fabricated according to the secondembodiment of the present invention.

As shown, the semiconductor light emitting device according to thesecond embodiment of the present invention comprises: a substrate 40formed of a silicon carbide (SiC), etc.; an n-type semiconductor layer41 formed on the substrate 40; a light emitting layer 42 formed on then-type semiconductor layer 41; a p-type semiconductor layer 43 formed onthe light emitting layer 42; a first transparent electrode 44 formed asa transparent electrode forming metal is deposited on the p-typesemiconductor layer 43 and then is patterned so that holes arerepeatedly formed per a certain region; a plate-type second transparentelectrode 45 formed on the first transparent electrode 44; and first andsecond pads 46 and 47 respectively formed on the second transparentelectrode 45 and on the rear surface of the substrate 40.

As aforementioned in the first and second embodiments of the presentinvention, a transparent electrode that facilitates a current spread tothe light emitting layer is formed on the p-type semiconductor layerthereby to reduce a contact resistance of the p-type semiconductorlayer. According to this, a driving voltage can be more lowered whencompared to the conventional art where a TCO-based transparent electrodeis used. Also, the transparent electrode is patterned thus to form aplurality of holes that expose a part of the p-type semiconductor layer,thereby increasing a light transmittance that light generated from thelight emitting layer is emitted to outside. According to this, whencompared to the conventional light emitting device where a conductivemetal such as Ni, Au, etc. is used as a transparent electrode, a lightemitting efficiency of the light emitting device of the presentinvention can be more increased.

In the first and second embodiments of the present invention, the n-typesemiconductor layer, the light emitting layer, and the p-typesemiconductor layer are formed of a nitride semiconductor. However, thepresent invention is not limited to the nitride semiconductor. That is,the present invention can include all light emitting devices that thetransparent electrode formed on the p-type semiconductor is formed of aconductive metal having a plurality of holes.

The present invention is to provide a semiconductor light emittingdevice capable of facilitating a current spread to the light emittinglayer from the transparent electrode by greatly reducing a contactresistance between the p-type semiconductor layer and the transparentelectrode.

That is, in case of forming the transparent electrode on the p-typesemiconductor layer by sequentially depositing Ni and Au in accordancewith the conventional art, NiO formed as said Ni is oxidized has aninferior conductivity thereby to shield a spread of a current suppliedfrom outside to the light emitting layer.

According to this, in the present invention, Ni and Au aresimultaneously deposited thus to prevent the metal oxide NiO from beingexcessively formed, thereby minimizing a restraint of a current spreadto the light emitting layer due to the metal oxide.

FIGS. 9A to 9D are processing section views showing a fabrication methodof a semiconductor light emitting device according to a third embodimentof the present invention to increase an ohmic characteristic between thep-type nitride semiconductor layer and the transparent electrode formedthereon.

As shown in FIG. 9A, first, a sapphire substrate 50 is prepared. Then, anitride semiconductor is grown on the substrate 50 with a certainthickness by using a metal organic vapor phase epitaxy growing method,etc. Then, an n-type impurity is doped thereby to form an n-typesemiconductor layer 51. Next, a light emitting material and a nitridesemiconductor layer are sequentially deposited on the n-typesemiconductor layer 51, then a p-type impurity is doped on the nitridesemiconductor thereby to form a p-type semiconductor layer 53.

The n-type semiconductor layer 51 can be formed with a thicknesscorresponding to 1 μm˜500 μm, approximately. As the n-type impurity, oneof Si, Ge, Se, S, Te, etc. can be selected. The p-type semiconductorlayer 53 may be formed with a thickness corresponding to 0.1 μm˜100 μm,approximately. As the p-type impurity, one of Be, Sr, Ba, Zn, Mg, etc.can be selected.

As shown in FIG. 9B, a mesa etching is partially performed from thep-type semiconductor layer 53 to the n-type semiconductor layer 51 in avertical direction, thereby exposing a part of the n-type semiconductorlayer 51.

Then, a metal group that at least one metal oxide generating metal andat least one current spreading metal are mixed is deposited on thep-type semiconductor layer 53, thereby forming a transparent electrode54 as shown in FIG. 9C.

That is, the transparent electrode 54 is formed by depositing a metalgroup that at least one metal oxide generating metal such as Ni, Pd, Pt,Pu, Ir, Zn, Mg and at least one current spreading metal such as Au aremixed on the p-type semiconductor layer 53. At this time, it is the mostpreferable to deposit a metal group that Ni and Au are mixed. Then, athermal annealing was performed in an atmosphere that a little amount ofoxygen is mixed to nitrogen at a temperature of 400° C.˜1000° C.,thereby facilitating an ohmic contact between the p-type semiconductorlayer 53 and the transparent electrode 54.

It is also possible to pattern the transparent electrode 54 thereby toform a plurality of holes 54a that expose a part of the p-typesemiconductor layer 53.

As aforementioned in the first and second embodiments of the presentinvention, the holes 54a minimize a shield of light generated from thelight emitting layer 52 by the transparent electrode 54, and enhance alight emission to outside. In the preferred embodiment, the holes can beformed or can not be formed. However, in case of forming the holes atthe transparent electrode 54, a light transmittance can be moreincreased than a case that the holes are not formed.

As shown in FIG. 9D, on the transparent electrode 54 and on the rearsurface of the substrate 50, one of Ni, Cr, Al, Au, Pt, Ti, etc. or amixture of at least two therebetween is deposited and then is patterned.According to this, a first pad 56 for electrically connecting thetransparent electrode 55 to an external terminal, and a second pad 57for electrically connecting the exposed n-type nitride semiconductorlayer 51 a to an external terminal are respectively formed.

Although not shown, a TCO-based transparent electrode can be furtherformed on the transparent electrode. In this case, the first and secondpads are formed on the TCO-based transparent electrode.

The fabrication method of a semiconductor light emitting device forforming a transparent electrode by simultaneously depositing a metaloxide generating metal and a current spreading metal on the p-typenitride semiconductor layer can be applied to a fabrication method of aTop-down electrode type semiconductor light emitting device.

FIGS. 10A to 10C are processing section views showing a fabricationmethod of a Top-down electrode type semiconductor light emitting deviceaccording to a fourth embodiment of the present invention.

As shown in FIG. 10A, an n-type semiconductor layer 61, a light emittinglayer 62, and a p-type semiconductor layer 63 are sequentially formed ona substrate 60. Said process is the same as that of the thirdembodiment.

Then, a metal group that at least one metal oxide generating metal suchas Ni, Pd, Pt, Pu, Ir, Zn, Mg and at least one current spreading metalsuch as Au are mixed is deposited on the p-type semiconductor layer 63,thereby forming a transparent electrode 64 as shown in FIG. 10B. At thistime, it is the most preferable to form the transparent electrode 64 bydepositing a metal group that Ni and Au are mixed and by performing athermal annealing in an atmosphere such as nitrogen or oxygen at atemperature of 300° C.˜1000° C.

The transparent electrode 64 can be fabricated as various shapes such asa stripe shape or a mesh stripe shape. In the present invention, theshape of the transparent electrode 64 is not limited to a specific one.

It is also possible to form the hole 64a that exposes a part of thep-type semiconductor layer 63 by patterning the transparent electrode 64like in the aforementioned embodiment.

Finally, as shown in FIG. 10C, on the transparent electrode 64 and onthe rear surface of the substrate 60, one of Ni, Au, Pt, Ti, etc. or amixture of at least two therebetween is deposited and then is patterned.According to this, a first pad 66 for electrically connecting thetransparent electrode 64 to an external terminal, and a second pad 67for electrically connecting the substrate 60 to an external terminal arerespectively formed.

Although not shown, a TCO-based transparent electrode can be furtherformed on the transparent electrode. In this case, the first and secondpads are formed on the TCO-based transparent electrode.

In the third and fourth embodiments of the present invention, a metalgroup that at least one metal oxide generating metal and at least onecurrent spreading metal are mixed is deposited on the p-typesemiconductor layer thereby to form the transparent electrode. At thetime of depositing the metal group, an interface between the p-typesemiconductor layer and the transparent electrode is oxidized, andthereby a metal oxide for supplying a hole to a p-GaN layer is generatedon the p-type semiconductor layer. At this time, due to more activeoxidization on the surface of the metal group, a metal oxide isrelatively less generated at the periphery of the interface whencompared to the conventional art.

That is, if the transparent electrode is formed by depositing a certainmetal group on the p-type semiconductor layer according to the third andfourth embodiments, a metal oxide generating metal constituting themetal group, for example, Ni is evenly distributed from the surface ofthe p-type semiconductor layer to the uppermost part of the transparentelectrode. According to this, the metal oxide can be more easily formedwhen compared to the conventional art.

Also, since a metal oxide is relatively less generated at the peripheryof the interface between the p-type semiconductor layer and thetransparent electrode when compared to the conventional art, a value ofan ohmic contact resistance becomes relatively less when compared to theconventional art thereby to facilitate an ohmic contact.

FIG. 11 is a view schematically showing a section structure of atransparent electrode formed on a p-type nitride semiconductor accordingto the third and fourth embodiments of the present invention.

First, GaN, III-V group compound is formed on a sapphire substrate or anSiC substrate. Next, a metal group that Ni and Au are mixed is depositedon the p-doped GaN layer, and then a thermal annealing is performed,thereby obtaining a transparent electrode.

As shown, if a metal group that Ni and Au are mixed is deposited andthen a thermal annealing is performed, Au of an island shape is formedon the p-doped GaN layer 76 and NiO is formed on the Au. When comparedto the conventional structure (Refer to FIG. 3), in the presentinvention, Au is more formed on the surface of the P-GaN 76, and NiO isless formed on the surface of the P-GaN 76.

As aforementioned in the conventional art, the metal oxide NiO suppliesa hole to the p-GaN 73, and the Au facilitates a spread of the holesupplied from the metal oxide to the light emitting layer. The fact thatthe contact area between the P-GaN and the Au was increased means that acurrent spread was more briskly performed when compared to theconventional art.

FIG. 12 is a graph showing a distribution of Au and NiO according to athickness of a transparent electrode according to the third and fourthembodiments of the present invention. In the experiment, a sapphiresubstrate was used as a substrate, a GaN, III-V group compound was usedas a nitride semiconductor, a metal group that Ni and Au are mixed wasdeposited on the p-doped GaN layer to form a transparent electrode, anda thickness of the transparent electrode was approximately 1 nm˜100 nm.Also, a thermal annealing for forming the transparent electrode wasperformed at a temperature of approximately 600° C., and an allowanceerror range of the temperature in the thermal annealing wasapproximately ±100° C. At this time, the thermal annealing was performedin an atmosphere that a little amount of oxygen is mixed to nitrogen,and a rapid thermal annealing (RTA) device was used for the thermalannealing.

As shown from the graph, Au is concentrated on the surface of the P-GaN,and NiO is decreased from the surface thereof to the interface betweenthe P-GaN and the NiO. At the interface between the P-GaN and the NiO,the NiO is less distributed than the Au.

That is, when compared to the conventional drawing (refer to FIG. 4), inthe semiconductor light emitting device according to the presentinvention, a metal oxide, NiO that is not required any longer if acertain amount thereof is satisfied is relatively less formed at theinterface between the p-GaN layer. The more the metal oxide, NiO isgenerated, the more a current spread to the light emitting layer isrestrained thereby to increase a driving voltage of a device and toreduce a lifespan of the device. However, in the present invention, themetal oxide, NiO is less generated at the interface between the P-GaNlayer, thereby lowering a driving voltage of the device and increasing alifespan of the device.

As aforementioned, in the nitride semiconductor light emitting deviceand the fabrication method thereof according to the third and fourthembodiments of the present invention, a metal oxide can be easily formedat the time of depositing a transparent electrode. Also, an excessivegeneration of the metal oxide is restrained thereby to facilitate acurrent spread to the light emitting layer. According to this, a drivingvoltage of the device is lowered and thus a lifespan of the device isincreased.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the metes and bounds of theclaims, or equivalence of such metes and bounds are therefore intendedto be embraced by the appended claims.

What is claimed is:
 1. A fabrication method of a semiconductor lightemitting device comprising: providing a substrate; forming an n-typesemiconductor layer, a light emitting layer, and a p-type semiconductorlayer on the substrate; forming a first transparent electrode on thep-type semiconductor layer, said first transparent electrode havingholes per a certain region to thereby expose the p-type semiconductorlayer; forming a first pad on the first transparent electrode; andforming a second transparent electrode on the first transparentelectrode.
 2. The method of claim 1, wherein the providing the substrateis performed by providing a sapphire substrate.
 3. The method of claim2, further comprising: performing a mesa-etching from the p-typesemiconductor layer to the n-type semiconductor layer partially in avertical direction, and thereby exposing a part of the n-typesemiconductor layer; and forming a second pad on the exposed n-typesemiconductor layer.
 4. The method of claim 1, wherein the providing thesubstrate is performed by providing a silicon carbide substrate.
 5. Themethod of claim 4 further comprising forming the second pad on a rearsurface of the silicon carbide substrate.
 6. The method of claim 1,wherein the forming a first transparent electrode is performed byselecting one from a group composed of Ni, Au, Pd, Pt, Ir, Zn, and Mg orby forming a mixture of at least two therebetween.
 7. The method ofclaim 1, wherein the forming the first transparent electrode comprises:forming a first metal layer by depositing a metal group that at leastone metal oxide generating metal and at least one current spreadingmetal are mixed on the p-type semiconductor layer; and annealing thefirst metal layer.
 8. The method of claim 7, wherein the metal oxidegenerating metal is one selected from a group composed of Ni, Pd, Pt,Ir, Zn, and Mg, or a mixture of at least two therebetween.
 9. The methodof claim 7, wherein the current spreading metal is Au.
 10. The method ofclaim 1, wherein the holes comprise empty spaces between pillars of thefirst transparent electrode.
 11. The method of claim 1, furthercomprising forming a second transparent electrode on the firsttransparent electrode.
 12. The method of claim 1, wherein the secondtransparent electrode is formed of one selected from a group composed ofITO, IZO, ZnO, AZO, CdO and MgO.
 13. A fabrication method of asemiconductor light emitting device comprising: providing a substrate;forming an n-type semiconductor layer, a light emitting layer, a p-typesemiconductor layer on the substrate; forming a first transparentelectrode having holes per a certain region on the p-type semiconductorlayer; forming a first pad on the first transparent electrode; andforming a second transparent electrode on the first transparentelectrode, wherein the forming a first transparent electrode comprises:forming a first metal layer by depositing a metal group that at leastone metal oxide generating metal and at least one current spreadingmetal are mixed on the p-type semiconductor layer; and annealing thefirst metal layer.
 14. The method of claim 13, wherein the secondtransparent electrode is formed of one selected from a group composed ofITO, IZO, ZnO, AZO, CdO, and MgO.
 15. A fabrication method of asemiconductor light emitting device comprising: providing a substrate;forming an n-type semiconductor layer, a light emitting layer, a p-typesemiconductor layer on the substrate; forming a first transparentelectrode having holes per a certain region on the p-type semiconductorlayer; and forming a second transparent electrode on the firsttransparent electrode, wherein the second transparent electrodecomprises a metal oxide.
 16. The method of claim 15, wherein the secondtransparent electrode is formed of one selected from a group composed ofITO, IZO, ZnO, AZO, CdO, and MgO.
 17. A fabrication method of asemiconductor light emitting device comprising: providing a substrate;forming an n-type semiconductor layer, a light emitting layer, and ap-type semiconductor layer on the substrate; depositing a metal groupthat at least one metal oxide generating metal and at least one currentspreading metal are mixed on the p-type semiconductor layer, and therebyforming a first transparent electrode; forming a first pad on the p-typesemiconductor layer; forming holes that expose the p-type semiconductorlayer per a certain region on the first transparent electrode; andforming a second transparent electrode on the first transparentelectrode.
 18. The method of claim 17, wherein the providing thesubstrate is performed by providing a sapphire substrate.
 19. The methodof claim 18, further comprising: performing a mesa-etching from thep-type semiconductor layer to the n-type semiconductor layer partiallyin a vertical direction, and thereby exposing a part of the n-typesemiconductor layer; and forming a second pad on the exposed n-typesemiconductor layer.
 20. The method of claim 17, wherein the providingthe substrate is performed by providing a silicon carbide substrate. 21.The method of claim 20, further comprising forming a second pad on arear surface of the silicon carbide substrate.
 22. The method of claim17, wherein the metal oxide generating metal is one selected from agroup composed of Ni, Pd, Pt, Ir, Zn, and Mg or a mixture of at leasttwo therebetween.
 23. The method of claim 17, wherein the currentspreading metal is Au.
 24. The method of claim 17, wherein the holescomprise empty spaces between pillars of the first transparentelectrode.
 25. The method of claim 17, further comprising forming asecond transparent electrode on the first transparent electrode.
 26. Themethod of claim 17, wherein the second transparent electrode is oneselected from a group composed of ITO, IZO, ZnO, AZO, CdO, and MgO. 27.A fabrication method of a semiconductor light emitting devicecomprising: providing a substrate; forming an n-type semiconductorlayer, a light emitting layer, a p-type semiconductor layer on thesubstrate; depositing a metal group that at least one metal oxidegenerating metal and at least one current spreading metal are mixed onthe p-type semiconductor layer, and thereby forming a first transparentelectrode; forming a first pad on the p-type semiconductor layer; andforming a second transparent electrode on the first transparentelectrode.
 28. The method of claim 27, wherein the second transparentelectrode is one selected from a group composed of ITO, IZO, ZnO, AZO,CdO, and MgO.
 29. A method of fabricating a semiconductor light emittingdevice, the method comprising: providing a substrate; forming a firsttype semiconductor layer on the substrate; forming a light emittinglayer on the first type semiconductor layer; forming a second typesemiconductor layer on the light emitting layer; forming a firsttransparent electrode on the second type semiconductor layer, the firsttransparent electrode having holes per a certain region to therebyexpose the second type semiconductor layer; forming a second transparentelectrode on the first transparent electrode; forming a first pad on thesecond transparent electrode; and forming a second pad over the firsttype semiconductor layer, wherein the first transparent electrode is inthe shape of columns with gaps therebetween on the second typesemiconductor layer, wherein the first type semiconductor layer is ann-type semiconductor layer, and the second type semiconductor layer is ap-type semiconductor layer, wherein the second transparent electrodecompletely covers the first transparent electrode and fills the gaps ofthe first transparent electrode, and wherein the first transparentelectrode includes at least one of a metal and a metal oxide.
 30. Themethod of claim 29, wherein the substrate is a sapphire substrate or asilicon carbide substrate.
 31. The method of claim 29, wherein athickness of the first transparent electrode is approximately 1 nm-100nm.
 32. The method of claim 29, wherein a thickness the first typesemiconductor layer is 1 μm-500 μm and a thickness of the second typesemiconductor layer is 0.1 μm-100 μm.